Power is supplied from a high frequency power supply to a load such as a plasma processing apparatus. An impedance of the load changes. In this case, in order to efficiently supply high frequency power to the load, an impedance matching device for matching the impedance of the case where the load side is viewed from the high frequency power supply, with an output impedance of the high frequency power supply is used (refer to, for example, Japanese Patent Application Laid-Open No. 2012-142285).
The impedance matching device described in Japanese Patent Application Laid-Open No. 2012-142285 includes a variable capacitor and is provided between the high frequency power supply and the load. In a variable capacitor, a plurality of series circuits are connected in parallel. In each series circuit, a capacitor is connected in series to PIN (P-Intrinsic-N) diode. The impedance matching device disclosed in Japanese Patent Application Laid-Open No. 2012-142285 switches on or off the PIN diode based on a control signal of a controller so as to adjust the capacitance of the variable capacitor. Thereby, impedance matching is achieved.
As a method performed in the case of periodically modulating the amplitude of the high frequency power, there is a method of synchronizing the adjustment of the capacitance of the variable capacitor with a modulation period, for example. In order to switch on or off the PIN diode at high speed, a PIN diode driving circuit also needs to turn on or off the driving current at high speed. In the case of turning on or off the driving current of the PIN diode at high speed, a phenomenon has been observed in which the PIN diode breaks down despite that loss derating is performed using a PIN diode having a sufficient withstand voltage.
Japanese Patent Application Laid-Open No. H08-18072 discloses occurrence of a dynamic avalanche effect regarding a high speed power diode for a flywheel. The dynamic avalanche effect is a phenomenon in which elements are damaged due to steep commutation and a high intermediate circuit voltage.
According to the description of Japanese Patent Application Laid-Open No. H08-18072, after the maximum value of the reverse recovery current due to the commutation of the flywheel diode appears, the second maximum value caused by the dynamic avalanche appears.